The proposed Collaborative Corneal Transplantation Studies (CCTS) consist of two multicenter studies of the effectiveness of histocompatibility matching in preventing corneal allograft rejection in high risk eyes. Eyes with corneal stroma vascularization or a history of corneal graft rejection will be eligible for the CCTS. The Crossmatch Study will test the effectiveness of negative donor-recipient cross-matching in preventing corneal graft rejection in high risk patients who have detectable lymphocytoxic antibodies. Eyes will be randomized to receive either a positively crossmatched donor cornea or a negatively crossmatched donor cornea. The HLA Matching Study will assess the effectiveness of varying degrees of HLA-A,B donor-recipient matching and of hLA-DR donor-recipient matching in preventing corneal graft rejection in patients without detectable lymphocytotoxic antibodies. Patients will assigned orneas with different degrees of HLA matching. In both studies, treatment assignment and patient follow-up will be performed in a double masked fashion. Patients will followed closely durin the first post-operative year with continued follow-up for two additional years. Patients will follow a standard topical steroid medication plan after surgery. The two studies will be carried out by a single study organization. The leading corneal transplant centers will work in collaboration with their local tissue typing laboratory and cornea procuring eye bank in recruiting approximately 800 patients and 2500 corneas for the CCTS over a three year period. A Central HLA Laboratory will oversee standardization among the laboratories. A Coordinating Center will serve as the central data collection, data analysis, and administrative center. This application is for the Coordinating Center. The Coordinating Center plays and integral role in design development, implementation, and analysis in multicenter studies.